In winding wires and feeding cables of devices for energizing the high frequency current (transformers, motors, reactors, induction heating devices, magnetic head devices and the like), usually copper is used as a wire material owing to the reasons, such as higher electrical conductivity, availability, and the like. In these devices, the eddy current loss occurs in the conductor due to the magnetic field generated by the high frequency current, and it follows that the alternating current (AC) resistance (also referred to as “high frequency resistance”) increases (the skin effect and the proximity effect increase) and thus, increases in the heat generation and power consumption occurs.
In general, for suppressing the increases of the skin effect and proximity effect, countermeasure is made by thinning an outer diameter of the electric wire and employing a litz wire with insulating coating (for example, refer to Patent Documents 1 to 5).
However, in the technical means of the prior arts, it becomes a common knowledge that it is difficult to work for removing the insulating layer in soldering process for connection, and there is a limit for thinning the outer diameter due to increase in a number of element wires. Moreover, since effective countermeasure has not been found for the wire diameter where the proximity effect is overwhelmingly dominant more than the skin effect, it becomes a common knowledge that there is a limit to the characteristic obtained by the countermeasure to thin the outer diameter. In addition, although the examples of countermeasure are presented in Patent Documents 1 to 5, since any of them is a kind of idea and lacks detail or specifics, it cannot be a valid countermeasure.
Additionally, it is known to use the electric wire having a higher volume resistivity than the copper wire in a specific frequency range where the high frequency resistance is equal to or less than the copper wire, by utilizing the fact that the proximity effect loss in the electric wire having the higher volume resistivity than the copper wire is smaller than copper wire (for example, refer to Patent Document 6). Further, formulation of the resistance due to the proximity effect is being studied (for example, refer to Non-Patent Documents 1 and 2).